Answer:
1- study the fossils of ancient land vertebrates
Step-by-step explanation:
Some scientists concluded after performing a number of experiments that the legs of modern land vertebrates evolved from the fins of ancient fish. With the passage of time evolution occurs within the body of organisms. These changes occurs due to the surrounding environmental condition of that organism. When the organisms live in water, fins were present but when they go to the land so these fins change into legs. This type of evidence is provided by the scientist after studying the remains of ancient land vertebrates.